2/26/2015 week1 Day2 Thermal Expansion and Latent Heats

this photo is that at the same time heatting a ring and a ball, the atom's graph. The atoms of ring come to outside and inside at the same time, it should be increasing of inside and outside diameters, but the atoms of the outside diameter has the more power to pull the inside diameter, so in fact, the inside and outside diameters are both increased. For the bll, heating it that makes the atoms go outside that makes the ball bigger.

When only heating the ring, like we talk about in the first photo, the ring's inside and outside diameters are increasing at the same time. So the ball can cross the ring.

then we talk about the 4 reasons that can make the bar bigger. and find the unit of α is (℃)^(-1).

these three photos are the experiment that if we heat a thing that one side is brass and the other side is invar, what will happen. and the first photo is that before the experiment that we guess that it will curve to the right. because the left is brass and brass's coefficient of volume expansion is larger. then the professor heats right side and the left side one by one and the ending is that it always curve to the right. 

then the professor put it in to the ice water , we guess this that it will curve to the left and the result is same like our guess. so we can know that because the coefficient of volume expansion depends that which side will curve.

 

then we begin an experiment about the linear thermal expansion. the first four photos are the equipment. we use vapor to heat the tube and use logger pro to find the coefficients of linear expansion of the tube.

We used the data of the ΔL, Lo, r, ΔT and θ to find the α of the aluminum rod.this is the process of calculating,we use the equation on the right side and the sitar we find in the logger pro to calculate the coefficient of linear expansion of the tube is 1.9*10^(-6)(℃)^(-1）.

this experiment is that put the ice in the water and use the equipment to heat for 5mins. the second photo is the graph about this experiment. the graph of the third photo is that our guess about the graph.

and the equations are that we find the m of the water if we use a power of 293W to heat water by 300s from 0 ℃ to 100℃， the slope is dT/dt IS 0.3495,and the matter is 209g.

these two photos are to find the pressure of the water if we are blowing the water to raise a certain height. we use the equation at the top of the photo.

this photo is to figue out that if there are ice and water in the same place, how much energy that need to use to heat to a special temperature. at that time, we can not forget that the energy of ice becoming water, and we use the equation: Q=mL. L is the heats of fusion or vaporization.

this is another example that to find how much ice we need to make 255g water from 12 ℃ to 0℃.

Conclusion:

Today in class, we focused on  the thermal expansion and latent heat and the idea of thermal expansion. The change in temperature cause objects to expand by doing  letting the ball go through, heating the aluminum rod and calculating its expansion in length, heating water mixing with ice.We did activities such as heating the steel ring to and to calculate the mass of water in the cup, doing some latent heat problems. The  melting or evaporation change happen in ice and water that is significant in determining the heat gained equal to the heat lost idea in changing systems. we learn the ideal gas law pv=nRT by using pressure, volume, and temperature.